1. Field of the Invention
This invention relates to communication that uses time division duplexing (TDD) for multiple communication channels. In particular, the invention relates to synchronizing the duplexing across the plural channels, and further to assigning slots for time division multiple access (TDMA) in those channels such that consumer provided equipment (CPE) dynamically switches channels.
2. Description of the Related Art
Time division duplexing (TDD) is a well-known technique for bi-directional communication over a single frequency channel. In TDD, the channel is temporally divided into alternating upstream and downstream frames. Communication between a base station and several consumer provided equipment (CPEs) can share a single TDD channel through use of time division multiple access (TDMA). In TDMA, the upstream frames and the downstream frames are subdivided into plural slots. The base station allocates these slots among the CPEs. At a start of each downstream frame (i.e., from the base station to the CPEs), the base station sends data to the CPEs about the slot allocation, usually using media access protocol (MAP) messages.
Sometimes, a base station communicates with plural CPEs using TDMA on plural channels. Conventionally, each CPE is assigned to a channel, and the CPE receive MAP and data bursts and sends data bursts only on its assigned channel. This arrangement is shown in FIG. 4.
CPEs A to H in FIG. 4 communicate using TDMA on channels A to D. Frames are not synchronized between channels, as illustrated by the staggered arrangement of the upstream and downstream frames between the channel.
In FIG. 4, CPEs A and B are assigned to channel A, CPEs C and D are assigned to channel B, CPEs E and F are assigned to channel C, and CPEs G and H are assigned to channel D. Thus, CPEs A and B receive downstream MAP and data bursts from a base station and send upstream data bursts to the base station on channel A. CPEs C and D receive downstream MAP and data bursts from the base station and send upstream data bursts to the base station on channel B. CPEs E and F receive downstream MAP and data bursts from the base station and send upstream data bursts to the base station on channel C. CPEs G and H receive downstream MAP and data bursts from the base station and send upstream data bursts to the base station on channel D.
As shown in FIG. 4, some of the channels are used to full capacity, preventing additional data from being sent or received on those channels. For example, CPEs A and B cannot send additional data to the base station on channel A because the upstream frame of the channel is already fully utilized. Likewise, CPE F cannot send or receive data using channel C because CPE E is fully utilizing channel C. At the same time, some of the slots in the channels in FIG. 4 are unused. Thus, conventional channel and slot allocation can be inefficient and can lead to communication delays.